Try and make sure your calliper mounting are both post mounts so that you can do quick calliper re-centering when you swap the wheels over, unless you build the wheels on identical hubs and rotors. Alternatively you might need to shim the rotor on one set to match the other.

What a horrible predicament! If i were to be forced kicking and screaming down this route i'd be looking at something like a Giant Trance or a Stumpy, at the moment i ride a Cotic Soul and a Spesh Pitch and as much as i love the Soul i couldn't have it as my only bike.

I only have 1 bike as don't see the point with having anymore as I only want to ride this bike, my Yeti ASR-5 with 140 talas, CK hubs on stans rims, reverb post with brooks saddle, xx gears with middleburn duo cranks and hope tech x2 brakes and riding on fat conti tyres. Never will wish for more.

With a lockout fork, of course, as you say. It's fast and light enough for XC. Did a great job leading a few laps of TwentyFour12 24hr solo (until I swapped bikes with a puncture and the rear mech exploded on the other).

I wouldn't bother with a second set of wheels and tyres, just pop a fast rolling tyre on the back, something like a Crossmark or a Saguaro with a reasonably solid centre rear tread. My experience is the faff of swapping cassettes, wheels, re-aligning brakes isn't worth it and the knobblies stay on. The cost of a full wheelset, spare discs, tyres, cassette pays for a lot of new rear tyres

I have a Pitch (with DHX5 coil and Lyriks) and a steel 456 and may have to reduce to n=1 . Thinking I might return the Pitch to something a bit lighter (RP23 and a nice 140mm fork) but could also go 456 only bit maybe a carbon one, mmm what to do!

Rob, If you had a chain wear indicator tool you would not need to swap the cassette over when changing wheels.
I run 2 sets of wheels on my Tinbred (both Hope sport hubs) and have not changed either cassette yet, after over 3 years of use and a couple of chains. I just swap the wheels over in seconds, though am toying with rebuilding the commuting wheels with 700c rims.

For a bit of road, dirt-road mix rides and singletrack, a good rigid 29er is hard to beat as an all-rounder. If you have sus forks for the off-road weekends even better, but the fun-factor of a rigid 29er may mean you're happy on the rigid forks all the time - depends on where you ride off-road and who you ride with really.

I have too many bikes and have bought a rigid 29er to replace my CX bike, my rigid SS MTB and potentially my 26" 120mm HT. Keep a FS for weekends away and use the 29er for all but long road rides. I can imagine being quite happy on it as an only bike if space dictated it.